The two most common means of transmitting power from a crankshaft for synchronously driving rotating members, such as cam shafts and balance shafts, are timing chains and belts. Timing chains require engine oil to operate. In comparison most timing belt applications require that no oil be present in the belt drive as the presence of oil can damage the belt and inhibit its intended purpose. Recent improvements in belts no longer require that a belt be sealed from the engine oil environment.
The recent improvement of belts to operate in oil, however poses other problems that need to be solved. One specific problem is properly tensioning the belt drive to keep the camshaft synchronized with the crankshaft. Should the camshaft or other synchronized driven crankshaft component no longer be properly synchronized with the crankshaft; catastrophic engine damage can result.
To transmit power through the belt from the rotating crankshaft one side of the belt is pulled around the crankshaft and is commonly referred to as the belt tight side by those skilled in the art. Conversely the other side is referred to as the belt slack side, since the belt is being pushed away from the crankshaft. It is important to provide tensioning to the slack side of the belt to prevent the belt from becoming unduly slack and thus causing a loss of synchronization between the crankshaft and the components rotated by the crankshaft. This loss of synchronization is commonly referred to as “tooth jump” or “ratcheting” by those skilled in the art.
Compounding the problem of eliminating belt slack to prevent “tooth jump” or “ratcheting” is excessive tensioner arm motion or vibration induced by the engine's angular vibration. Excessive arm motion could not only lead to a “tooth jump” or a “ratcheting” condition, but can also reduce the useful life of the tensioner and the belt as well. To minimize the amount of arm vibration; friction damping is commonly used to prevent the tensioner from moving away from the belt.
The presence of oil makes friction damping difficult to achieve. One can appreciate that the application of a lubricant to two rubbing surfaces will allow relative motion between the two surfaces to occur more easily.
The important aspect of friction damping is the resistant torque generated by friction damping to resist the motion of the arm away from the belt. It is desirable to only have asymmetric damping where the arm motion is resisted only when the tensioner moves away from the belt and not towards the belt as in the prior art for tensioners that operate in a dry environment.
Representative of the art is U.S. Pat. No. 5,919,107 which discloses a A belt tensioner for tensioning a drive belt or timing belt comprises an eccentric adjusting member having an end surface thereof constructed and arranged to be mounted directly in surface-to-surface engagement with respect to a belt tensioner mounting surface for an engine frame. A pivoted structure is mounted on the eccentric adjusting member for pivoted movement between a first position and a second position, and a belt tensioning pulley is mounted for rotational movement on the pivoted structure. A coil torsion spring is constructed and arranged to resiliently bias the pivoted structure in a belt tightening direction away from the first position and toward the second position, the eccentric adjusting member being movable during an installation procedure to move the pivoted structure against the bias of the coil torsion spring into a position wherein the belt tensioning pulley is disposed in predetermined static tensioning relation with the belt, at which point the eccentric adjusting member is to be manually fixed. The end surface of the eccentric adjusting member is in sliding surface-to-surface relation with the mounting surface during rotation of the eccentric adjusting member.
What is needed is a tensioner comprising friction damping for use in oil using an elastomeric damping ring friction element having a friction force and a retaining member connected to an adjuster and cooperatively engaged with the sleeve whereby the adjuster and sleeve are kept in a predetermined relation. The present invention meets this need.